System for recapturing energy lost to plasma or ionization heating

ABSTRACT

A system for recapturing energy may include a thermoelectric generator (TEG) assembly for thermally attaching to a surface heated by plasma or ionization heating. The TEG assembly may include a first level thermoelectric generator module (TEM). The first level TEM may include a hot side that is thermally attached to the surface, a cold side and a plurality of TEG devices disposed between the hot side and the cold side. A second level TEM may be stacked on the first level TEM. A hot side of the second level TEM may be thermally attached to the cold side of the first level TEM. The plurality of TEG devices generate an electric current based on a temperature differential across the TEG devices. The TEG assembly may also include an electrical wiring system that electrically connects the TEMs and supplies the electric current generated to an electrical power apparatus.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is related to U.S. patent application Ser. No.14/952,166, filed Nov. 25, 2015, entitled “Thermal Electric AssemblyAttached on an Outer Surface of a Hot Section of a Gas Turbine Engine toGenerate Electrical Power” which is assigned to the same assignee as thepresent application and is incorporated herein by reference.

FIELD

The present disclosure relates to recapturing energy that would be lost,and more particularly to a system for recapturing energy lost to plasmaheating or ionization heating.

BACKGROUND

A substantial amount of energy is lost because of heat dissipationassociated with thrusters or engines for propulsion of spacecraft,aircraft or other vehicles. Such vehicles, particularly spacecraft, forexample satellites, also use batteries to provide electrical power tothe vehicle or spacecraft. These batteries are typically charged orre-charged by solar energy. Accordingly, the battery capacity orrequirements may have to be considerably high to continuously power thespacecraft during long periods when sunlight or solar energy is notavailable. For example, the spacecraft may go into an eclipse, a solarpanel may become permanently malfunctioning, or the efficiency of asolar cell will degrade over the lifetime of the orbit or during protonbombardment while in transfer orbit through the inner Van Allen belt.This causes an in increase in weight onboard the vehicle or spacecraftfor additional battery capacity and the additional batteries occupyadditional volume onboard the vehicle or spacecraft. Additionally, anincreased number of solar arrays may also be required which necessitateadditional volume onboard the spacecraft and a further increase inweight onboard the vehicle. Accordingly, there is a need to recaptureenergy lost because of heat dissipation to reduce battery capacity andsolar cell requirements.

SUMMARY

In accordance with an embodiment, a system for recapturing energy mayinclude a thermoelectric generator assembly configured for thermallyattaching to a surface heated by one of plasma heating or ionizationheating. The thermoelectric generator assembly may include a first levelthermoelectric generator module. The first level thermoelectricgenerator module may include a hot side that is thermally attached tothe surface, a cold side opposite to the hot side and a plurality ofthermoelectric generator devices disposed between the hot side and thecold side. The plurality of thermoelectric generator devices generatesan electric current based on a temperature differential across each ofthe plurality of thermoelectric generator devices. The thermoelectricgenerator assembly may also include a second level thermoelectricgenerator module stacked on the first level thermoelectric generatormodule. The second level thermoelectric generator module may include ahot side thermally attached to the cold side of the first levelthermoelectric generator module, a cold side opposite to the hot sideand a plurality of thermoelectric generator devices disposed between thehot side and the cold side. The plurality of thermoelectric generatordevices generates an electric current based on a temperaturedifferential across each of the plurality of thermoelectric generatordevices. The thermoelectric generator assembly may also include anelectrical wiring system that electrically connects the second levelthermoelectric generator module to the first level thermoelectricgenerator module and supplies the electric current generated by thefirst level thermoelectric generator module and the second levelthermoelectric generator module to an electrical power apparatus.

In accordance with another embodiment, a system for recapturing energymay include a thruster including a nozzle. The nozzle may be heated byplasma heating or ionization heating of propellant gases beingdischarged through the nozzle. The system may include a plurality ofthermoelectric generator assemblies. Each thermoelectric generatorassembly may include a first level thermoelectric generator module. Thefirst level thermoelectric generator module may include a hot sidethermally attached to an exterior surface of the nozzle, a cold sideopposite to the hot side and a plurality of thermoelectric generatordevices disposed between the hot side and the cold side. The pluralityof thermoelectric generator devices generates an electric current basedon a temperature differential across each of the plurality ofthermoelectric generator devices. The thermoelectric generator assemblymay also include a second level thermoelectric generator module stackedon the first level thermoelectric generator module. The second levelthermoelectric generator module may include a hot side thermallyattached to the cold side of the first level thermoelectric generatormodule, a cold side opposite to the hot side and a plurality ofthermoelectric generator devices disposed between the hot side and thecold side. The plurality of thermoelectric generator devices generatesan electric current based on a temperature differential across each ofthe plurality of thermoelectric generator devices. The thermoelectricgenerator assembly may also include an electrical wiring system thatelectrically connects the plurality of thermoelectric generatorassemblies to a power management system.

In accordance with a further embodiment, a method for recapturing energymay include thermally attaching a plurality of thermoelectric generatormodules to an exterior surface a nozzle of a thruster. The nozzle may beheated by plasma heating or ionization heating of propellant gases beingdischarged through the nozzle. Each thermoelectric generator module mayinclude a first level thermoelectric generator module. The first levelthermoelectric generator module may include a hot side thermallyattached to an exterior surface of the nozzle, a cold side opposite tothe hot side and a plurality of thermoelectric generator devicesdisposed between the hot side and the cold side. The plurality ofthermoelectric generator devices generates an electric current based ona temperature differential across each of the plurality ofthermoelectric generator devices. The thermoelectric generator assemblymay also include a second level thermoelectric generator module stackedon the first level thermoelectric generator module. The second levelthermoelectric generator module may include a hot side thermallyattached to the cold side of the first level thermoelectric generatormodule, a cold side opposite to the hot side and a plurality ofthermoelectric generator devices disposed between the hot side and thecold side. The plurality of thermoelectric generator devices generatesan electric current based on a temperature differential across each ofthe plurality of thermoelectric generator devices. The thermoelectricgenerator assembly may additionally include an electrical wiring systemthat electrically connects the plurality of thermoelectric generatorassemblies to a power management system. The method may also includecapturing waste heat from the nozzle by the plurality of thermoelectricgenerator assemblies and converting the captured waste heat by theplurality of thermoelectric generator assemblies into electrical power.

In accordance with another embodiment or any of the previousembodiments, a third level thermoelectric generator module may bestacked on the second level thermoelectric generator module. The thirdlevel thermoelectric generator module may include a hot side thermallyattached to the cold side of the second level thermoelectric generatormodule, a cold side opposite the hot side and a plurality ofthermoelectric generator devices disposed between the hot side and thecold side. The plurality of thermoelectric generator devices generatesan electric current based on the temperature differential across theplurality of thermoelectric generator devices. The third levelthermoelectric generator module is electrically connected to the secondlevel thermoelectric generator module by the electrical wiring systemand the first level thermoelectric generator module, the second levelthermoelectric generator module and the third level thermoelectricgenerator module are arranged in a triple stack configuration using apyramid geometry for increased temperature differential across each ofthe thermoelectric generator modules. An area of the hot side and thecold side of each of the thermoelectric generator modules decreases fromthe first level thermoelectric generator module to the third levelthermoelectric generator module.

In accordance with another embodiment or any of the previousembodiments, each of the first level, second level and third levelthermoelectric generator modules may include a different type ofthermoelectric generator device based on a efficiency in convertingthermal energy to electrical energy accordingly to a temperature on thehot side of each respective thermoelectric module and a temperaturedifferential between the hot side and the cold side of each respectivethermoelectric generator module.

In accordance with another embodiment or any of the previousembodiments, a layer of material may be applied to cover thethermoelectric generator modules and at least a portion of theelectrical wiring system. The layer of material may be configured toprotect the system from radiation and moisture and to preventelectrostatic discharge from the system.

In accordance with another embodiment or any of the previousembodiments, the thermoelectric generator modules may each include acurved configuration that corresponds to a contour of the surface towhich the thermoelectric generator assembly is thermally attached.

In accordance with another embodiment or any of the previousembodiments, the thermoelectric generator modules may include flexiblematerials that allow the thermoelectric generator modules to flex withany movement of the surface.

BRIEF DESCRIPTION OF THE DRAWINGS

The following detailed description of embodiments refers to theaccompanying drawings, which illustrate specific embodiments of thedisclosure. Other embodiments having different structures and operationsdo not depart from the scope of the present disclosure.

FIG. 1 is side view of an example of a nozzle of a thruster including asystem for recapturing energy in accordance with an embodiment of thepresent disclosure.

FIG. 2 is a partial end view of the nozzle of the thruster showing adetailed view of a thermoelectric generator assembly in accordance withan embodiment of the present disclosure.

FIG. 3 is a perspective view of the thermoelectric generator assembly inFIG. 2.

FIG. 4 is a graph illustrating an efficiency of different n-typethermoelectric generator materials at different temperatures inaccordance with an embodiment of the present disclosure.

FIG. 5 is a graph illustrating an efficiency of different p-typethermoelectric generator materials at different temperatures inaccordance with an embodiment of the present disclosure.

FIG. 6 is a schematic diagram of an example of a spacecraft including athruster nozzle and a system for recapturing energy in accordance withan embodiment of the present disclosure.

FIG. 7 is a flow chart of an example of a method for recapturing energyin accordance with an embodiment of the present disclosure.

DETAILED DESCRIPTION

The following detailed description of embodiments refers to theaccompanying drawings, which illustrate specific embodiments of thedisclosure. Other embodiments having different structures and operationsdo not depart from the scope of the present disclosure. Like referencenumerals may refer to the same element or component in the differentdrawings. Although the disclosure is intended for space-based thrusters,the disclosure does not limit the use to spacecraft.

Certain terminology is used herein for convenience only and is not to betaken as a limitation on the embodiments described. For example, wordssuch as “proximal”, “distal”, “top”, “bottom”, “upper,” “lower,” “left,”“right,” “horizontal,” “vertical,” “upward,” and “downward”, etc.,merely describe the configuration shown in the figures or relativepositions used with reference to the orientation of the figures beingdescribed. Because components of embodiments can be positioned in anumber of different orientations, the directional terminology is usedfor purposes of illustration and is in no way limiting. It is to beunderstood that other embodiments may be utilized and structural orlogical changes may be made without departing from the scope of thepresent invention. The following detailed description, therefore, is notto be taken in a limiting sense, and the scope of the present inventionis defined by the appended claims.

FIG. 1 is side view of an example of a nozzle 100 of a thruster 102including a system 104 for recapturing energy in accordance with anembodiment of the present disclosure. Examples of the thruster 102 mayincluding but is not limited to electromagnetic thrusters, electrostaticthrusters, electrothermal thrusters, air-breathing engines or similarapparatus for propulsion of a vehicle, such as a spacecraft, aircraft,rocket or other type vehicle. Examples of electromagnetic thrusters mayinclude, but is not limited to, magnetoplasmadynamic (MPD) thrusters(MPDT), pulsed plasma thrusters (PPT), and Hall-effect thrusters (HET).Examples of electrostatic thrusters may include, but is not limited to,ion thrusters, colloaid thrusters, and field-emission electricpropulsion (FEEP) thrusters. Examples of electrothermal thrusters mayinclude, but is not limited to, microwave thrusters, magnetic nozzlethrusters, resistojets and arcjets. Examples of air-breathing enginesmay include, but is not limited to, turbojets, ramjets and scramjets.The system 104 for recapturing energy, as described herein, may beconfigured for capturing heat from plasma heating or ionization heatingby the thruster 102. However, the system 104 for recapturing energy isnot intended to be limited by the exemplary application described hereinand those skilled in the art will recognize that the system 104 may beconfigured for other applications and uses.

The nozzle 100 may be substantially cone shaped including an intake 106or input opening at a smaller radius end of the cone-shaped nozzle 100and an exhaust 108 at a wider radius end of the nozzle 100. Acceleratingpropulsion gases enter the nozzle 100 from a combustion chamber 110 viathe intake 106 and escape via the exhaust 108 for propulsion of thevehicle to which the thruster 102 is attached, for example, spacecraft600 in FIG. 6. The exhaust 108 of the nozzle 100 may have a radius R1about an axis X of the nozzle 100. The axis X may define a centerlinealong a longitudinal length of the nozzle 100 from the intake 106 to theexhaust 108. An internal radius of the nozzle 100 in a plane through theaxis X may vary from the intake 106 to the exhaust 108 of the nozzle100. The internal radius of the nozzle 100 is smallest at the intake 106and gradually increases toward the exhaust 108 where the radius of thenozzle 100 may be largest. In an embodiment, an interior surface 112 andan exterior surface 114 of the nozzle 100 may be linear in alongitudinal direction along the axis X between the intake 106 and theexhaust 108. In another embodiment, the interior surface 112 and theexterior surface 114 of the nozzle 100 may be curved in the longitudinaldirection along the axis X or in plane corresponding to the axis Xbetween the intake 106 and the exhaust 108. Accordingly, the interiorsurface 112 and exterior surface 114 of the nozzle 100 may have radiithat vary in at least two directions, circumferentially about the axis Xand longitudinally along the axis X between the intake 106 and theexhaust 108 of the nozzle 100. For example, radius R1 extendscircumferentially about the axis X and radius R2 (FIG. 3) that definesan arc between the intake 106 and the exhaust 108. The radius R1 may bereferred to as a radial radius and the radius R2 may be referred to asan axial radius of the nozzle 100.

The system 104 for recapturing energy may include at least onethermoelectric generator assembly 116 configured for thermally attachingto a surface heated by one of plasma heating or ionization heating. Inthe example illustrated in FIG. 1, the system 104 for recapturing energyincludes a plurality of thermoelectric generator assemblies 116 that arethermally attached to the exterior surface 114 of the nozzle 100. Eachof the plurality of thermoelectric generator assemblies 116 may bebonded to the exterior surface 114 of the nozzle 100 by a thermallyconductive bonding agent 126 (FIG. 2), adhesive or other arrangement forthermally attaching the thermoelectric generator assemblies 116 to thenozzle 100. As previously discussed, the nozzle 100 may be heated byplasma heating or ionization heating of propellant gases acceleratingthrough the nozzle 100 and being discharge through the exhaust 108. Theenergy lost due to plasma heating and ionization may be modeled by theequation 1:

$\begin{matrix}{{VJ} = {{\int_{V}{\frac{j^{2}}{\sigma}\ d\; V{\int_{V}{{ujB}\mspace{11mu} d\; V}}}} + {V_{E}J}}} & {{Equation}\mspace{14mu} 1}\end{matrix}$

Equation 1 is from course notes entitled Physics of Plasma Propulsion byProfessor Edgar Choueiri, Department of Mechanical and AerospaceEngineering, Princeton University, Princeton, N.J. 2015. The first termof equation 1 is the sum of energy lost to heating; a percentage of thisenergy will be recaptured through the system 104.

Referring also to FIG. 2, FIG. 2 is a partial end view of the nozzle 100of the thruster 102 showing a detailed view of a thermoelectricgenerator assembly 116 in accordance with an embodiment of the presentdisclosure. Each thermoelectric generator assembly 116 may include afirst level thermoelectric generator module (TEM) 118. The first levelTEM 118 may include a hot side 120 that is thermally attached to theexterior surface 114 of the nozzle 100, a cold side 122 opposite to thehot side 120 and a plurality of thermoelectric generators (TEG) or TEGdevices 124 disposed between the hot side 120 and the cold side 122. Thehot side 120 of the first level TEM 118 may be thermally attached to theexterior surface 114 of the nozzle 100 by a thermally conductive bondingagent 126, adhesive or other arrangement that thermally transfers heatfrom the exterior surface 114 of the nozzle 100 to the hot side 120 ofthe first level TEM 128 with minimal if any heat dissipation or loss.The plurality of TEG devices 124 generates an electric current based ona temperature differential across each of the plurality of TEG devices124 or a temperature gradient between the hot side 120 and the cold side122.

Each thermoelectric generator assembly 116 may also include a secondlevel TEM 128 stacked on the first level TEM 118. The second level TEM128 may include a hot side 130 that is thermally attached to the coldside 122 of the first level TEM 118, a cold side 132 opposite to the hotside 130 and a plurality of TEG devices 134 disposed between the hotside 130 and the cold side 132. The hot side 130 of the second level TEM128 may be thermally attached to the cold side 122 of the first levelTEM 118 by a thermally conductive bonding agent 126, adhesive or otherarrangement that thermally transfers heat from the cold side 122 to thehot side 130 of the second level TEM 128 with minimal if any heatdissipation loss. The plurality of TEG devices 134 also generates anelectric current based on a temperature differential across each of theplurality of TEG devices 134. The second level TEM 128 may beelectrically connected to the first level TEM 118 by electricalconductors 162 and 164 as best shown in FIG. 3. The first level TEM 118and the second level TEM 128 may be electrically connected in series.

In accordance with an embodiment, each thermoelectric generator assembly116 may also include at least a third level TEM 138 stacked on thesecond level TEM 128. The third level TEM 138 may include a hot side 140that is thermally attached to the cold side 132 of the second level TEM128, a cold side 142 opposite the hot side 140 and a plurality of TEGdevices 144 disposed between the hot side 140 and the cold side 142. Thehot side 140 of the third level TEM 138 may be thermally attached to thecold side 132 of the second level TEM 128 by a thermally conductivebonding agent 126, adhesive or other arrangement that thermallytransfers heat from the cold side 132 to the hot side 1140 of the thirdlevel TEM 144 with minimal if any heat dissipation or loss. Theplurality of TEG devices 144 generates an electric current based on atemperature differential across the plurality of TEG devices 144 ortemperature gradient between the hot side 140 and cold side 142 of thethird level TEM 138. The third level TEM 138 may be electricallyconnected to the second level TEM 128 by electrical conductors 162 and164 (FIG. 3). The first level TEM 118, second level TEM 128 and thirdlevel TEM 138 may be electrically connected in series.

A thermally conductive device 146 may be thermally attached to the coldside 142 of the third level TEM 138. The thermally conductive device 146may be configured for connection to a thermal management system 148. Thethermally conductive device 146 and thermal management system 148 maycreate a larger temperature differential between the hot side 120 of thefirst level TEM 118 and the cold side 142 of the third level TEM 138 toincrease efficiency of converting the heat energy to electrical energyby the thermoelectric generator assembly 116. The thermally conductivedevice 146 may be thermally attached to the cold side 142 of the thirdlevel TEM 138 by a thermally conductive bonding agent 126, adhesive orother arrangement that thermally transfers heat from the cold side 142of the third level TEM 138 to the thermally conductive device 146 withminimal if any heat dissipation. The thermally conductive device 146 maybe a heat energy conducting strap, referred to in the industry as a“thermal strap,” or other arrangement to transfer heat from thethermoelectric generator assembly 116 to the thermal management system148 for efficient conversion of heat or thermal energy to electricalenergy by the thermoelectric generator assembly 116.

A layer 168 of material (FIG. 1) may cover the thermoelectric generatorassemblies 116 and at least a portion of the electrical wiring system158. The layer 168 of material is not shown as covering thethermoelectric generator assemblies 116 in FIG. 1 so that thethermoelectric generator assemblies 116 are visible. The layer 168 ofmaterial may include properties and may be configured or applied toprotect the system 104 from radiation and moisture. The layer 168 ofmaterial may also include properties to prevent electrostatic dischargefrom the system 104 or electrostatic discharge protection properties. Anexamples of the layer 168 of material may include a glop top epoxyconfigured and/or including properties for purposes including but notlimited to radiation hardening and structural mode suppression, otheraerospace material, including but not limited to, thermal blankets,protective silicon oxide (SiO₂) coating, micro-lattice structure forpurposes including but not limited to electromagnetic (EM) radiationprotection via Faraday Effect or other similar materials.

Referring also to FIG. 3, FIG. 3 is a perspective view of thethermoelectric generator assembly 116 in FIG. 2. The first level TEM118, second level TEM 128 and third level TEM 138 may be arranged in atriple stack configuration 152 using a pyramid geometry 154 forincreased temperature differential across each of the TEMs 118, 128 and138. An area 156 a, 156 b and 156 c of the hot side and the cold side ofeach of the TEMs 118, 128 and 138 may decrease from the first level TEM118 to the third level TEM 138. The first level TEM 118 may include acurved configuration that corresponds to a contour of the exteriorsurface 114 of the nozzle 100. The second level TEM 128 and the thirdlevel TEM 138, if provide, may also each include a curved configurationthat corresponds to the adjacent level TEM. Accordingly, the first levelTEM 118, second level TEM 128 and third level TEM 138, if provided, eachinclude a curved configuration that corresponds to the exterior surface114 of the nozzle 100 for efficient heat transfer from the exteriorsurface 114 of the nozzle 100 and through the TEMs 118, 128 and 138 forefficient conversion of the heat or thermal energy to electrical energy.The TEMs 118, 128 and 138 may be formed from flexible materials thatallow the TEMs 118, 128 and 138 to flex with any movement of theexterior surface 114 of the nozzle 100. For example, the materials maybe any substances that permit the TEMs 118, 128 and 138 orthermoelectric generator assembly 116 to flex without the TEMthermoelectric generator assembly 116 breaking down or coming apart orbeing unable to function as described herein.

Each of the TEG devices 124, 134 and 144 may include one or more p-dopedsemiconductors 157 and one or more n-doped semiconductors 159 orthermoelectric generator materials as described with reference to FIGS.4 and 5. The semiconductors 157 and 159 or crystals may be shaped ineach layer or level TEM 118, 128 and 138 so that each thermoelectricgenerator module 116 matches or corresponds to the contour of theexterior surface 114 of the nozzle 100 at whatever location a particularthermoelectric generator module 116 may be located. As previouslydescribed and as illustrated in FIG. 3, the exterior surface 114 of thenozzle 100 may have radii that vary in at least two directions,circumferentially about the axis X (FIG. 1) or radial radius R1 andlongitudinally along the axis X between the intake 106 and the exhaust108 of the nozzle 100 or axial radius R2. The semiconductors 157 and 159of each thermoelectric generator assembly 116 may be shaped to match theradii of curvature or radial radius R1 and axial radius R2 of theexterior surface 114 of the nozzle 100 at the particular location wereeach thermoelectric generator assembly 116 may be placed to provideefficient conversion of heat energy to electrical energy with minimalheat loss or dissipation. The semiconductors 157 and 159 may be shapedby any process used to shape or form semiconductor materials, such asablation, chemical vapor deposition, or other processes for adding,removing or shaping material.

An electrical wiring system 158 (FIG. 1) may electrically connect theplurality of thermoelectric generator assemblies 116 to an electricalpower apparatus 160. The electrical power apparatus 160 may be a powermanagement system, power distribution system or both. Eachthermoelectric generator assembly 116 may include electrical conductors162 and 164 (FIG. 3) that electrically connect the third level TEM 138to the second level TEM 128 and the second level TEM 128 to the firstlevel TEM 118. The electrical conductors 162 and 164 from each level TEM118, 128 and 138 may connect to a power bus 166 (FIG. 1). The power bus166 supplies the electric current generated by the TEMs 118, 128 and 138to the electrical power apparatus 160. The thermoelectric generatorassemblies 116 may be electrically connected in series.

As previously described, each thermoelectric generator assembly 116 mayinclude a plurality of thermoelectric generators (TEG) or TEG devices124, 134 and 144 that generate an electric current based on atemperature differential across each of the plurality of TEG devices124, 134 and 144. A TEG or TEG device 124, 134 and 144 can generateelectricity when a temperature differential is applied or exists acrossthe device. The TEG device 124, 134 or 144 may typically be square orrectangular shaped with an upper and lower end-cap having the samedimension. Typically power generated by TEGs is transmitted via a set ofelectrical conductors 162 and 164 or a power bus 166 similar to thatdescribed herein with reference to FIG. 1. TEG devices 124, 134 and 144are typically thin (e.g., on the order of a couple of millimetersthick), small (e.g., a couple of square centimeters), flat, and brittle.Accordingly, TEG devices 124, 134 and 144 can be difficult to handleindividually, especially for applications on thruster nozzles asdescribed herein and vehicles, such as spacecraft, aircraft, automobilesand the like, where the TEG devices 124, 134 and 144 can be subject toharsh environmental conditions, such as vibration, constant temperaturevariations and other harsh conditions. Because of their size and thefact that each TEG device 124, 134 and 144 generates only a small amountof power, many TEG devices 124, 134 and 144 are bundled together inorder to generate a useful amount of power. Further, TEG devices 124,134 and 144 generally provide greater energy conversion efficiency athigh temperature. This can cause relatively large thermal expansion inmaterials. Because of thermal gradients and different thermalcoefficients of expansion associated with different materials, thermallyinduced stresses may result. Efficiency of TEG devices 124, 134 and 144generally increases with greater temperature differentials, i.e., deltatemperature between two opposite sides, typically called the heat sourceor hot side 120 and heat sink or cold side 122 of the TEG device 124 inthe first level TEM 118. Also, energy conversion efficiency is maximizedfor any installation that channels heat flow through the TEG devices124, 134 and 144 only without any thermal energy leaks through thesurrounding structural material or gaps. Thus, to simplify handling andachieve high performance in converting heat to electricity, multiple TEGdevices 124, 134 and 144 can be encased into a module such as TEMs 118,128 and 138 and an assembly, such as assembly 116 prior to finalinstallation.

As previously described, the temperature of the exterior surface 114 ofthe nozzle 100 may vary along the nozzle 100. The TEG devices 124, 134and 144 may include different materials that may be used in differentheat zones 170 a-170 c (FIG. 1) along the nozzle 100 between thecombustion chamber 110 and the exhaust 108 of the nozzle 100. Forexample, a temperature of the exterior surface 114 of the nozzle 100 maybe hottest at an exhaust of the combustion chamber 110 or intake 106 ofthe nozzle 100 and the temperature of the exterior surface 114 maygradually decrease along the nozzle 100 toward the exhaust 108.

Additionally, each of the first level, second level and third level TEMs118, 128 and 138 may include a different type of TEG device 124, 134 and144. The different types of TEG devices 124, 134 and 144 of each of thefirst level, second level and third level TEMs 118, 128 and 138 may beconfigured to generate a predetermined level of electrical power basedon a temperature on the hot side of each respective TEM 118, 128 and 138and a temperature differential between the hot side and the cold side ofeach respective TEM 118, 128 and 138. Each of the first level, secondlevel and third level TEMs 118, 128 and 138 may include the differenttypes of TEG device 124, 134 and 144 based on an efficiency inconverting thermal energy to electrical energy according to atemperature on the hot side of each respective level TEM 118, 128 and138 and a temperature differential between the hot side and the coldside of each respective level TEM 118, 128 and 138.

Referring also to FIG. 4 and FIG. 5, FIG. 4 is a graph 400 illustratingan efficiency of different n-type thermoelectric generator materials atdifferent temperatures in accordance with an embodiment of the presentdisclosure. FIG. 5 is a graph 500 illustrating an efficiency ofdifferent p-type thermoelectric generator materials at differenttemperatures in accordance with an embodiment of the present disclosure.The graphs 400 and 500 show ZT for TEG devices composed of differentmaterials over temperatures from 0 degrees C. to 1000 degrees C. ZT is adimensionless figure of merit that corresponds to an ability of a givenmaterial or combination of materials to efficiently produce electricpower. ZT may be defined by equation 2:

$\begin{matrix}{{ZT} = \frac{\sigma \; S^{2}T}{\lambda}} & {{Equation}\mspace{14mu} 2}\end{matrix}$

Where S is the Seebeck coefficient, λ is the thermal conductivity of thematerial or materials, σ is the electrical conductivity and T is thetemperature. The higher ZT for a particular TEG device composed of acertain material or materials at a particular temperature or temperaturerange, the more efficient the TEG device composed of those materials isat generating electrical power at the particular temperature ortemperature range. Accordingly, thermoelectric generator assemblies 116that include different type TEG device 124, 134 and 144 that have ahigher ZT or a higher efficiency of generating electrical power may beused at certain locations along the along the nozzle 100 based on atemperature of the exterior surface 114 of the nozzle 100 duringoperation of the thruster 102.

In accordance with an embodiment, the plurality of thermoelectricgenerator assemblies 116 may be distributed along the exterior surface114 of the nozzle 100 at predetermined locations between the intake 106and the exhaust 108 to maximize electrical power generation. Theplurality of thermoelectric generator assemblies 116 may includedifferent types of TEG devices 124,134 and 144, each different type ofTEG device 124, 134 and 144 may be formed from a particular material orparticular group of materials configured to provide a highest efficiencyof thermal energy to electrical energy conversion based on a temperatureof the exterior surface 114 of the nozzle 100, during operation of thethruster 102, where each of the plurality of thermoelectric generatorassemblies 116 is located between the intake 106 and the exhaust 108.Therefore, the different types of TEG devices 124, 134 and 144 may beconfigured to generate a predetermined level of electrical power basedon a temperature of the exterior surface 114 of the nozzle 100 at thepredetermined location of the TEG assembly 116 during operation of thethruster 102.

FIG. 6 is a schematic diagram of an example of a spacecraft 600including a thruster nozzle 602 and a system 604 for recapturing energyin accordance with an embodiment of the present disclosure. The system604 for recapturing energy may be similar to the system 104 describedwith reference to FIGS. 1-3 The system 604 for recapturing energy mayinclude a plurality of thermoelectric generator assemblies 606. Thethermoelectric generator assemblies 606 may be similar to thethermoelectric generator assemblies 116 described herein. An electricalwiring system 607 may electrically connect the thermoelectric generatorassemblies 606 to a power management system 608. The thermoelectricgenerator assemblies 606 may be electrically connected in series. Theelectrical wiring system 607 may include a power bus 610 that connectsthe thermoelectric generator assemblies 606 to the power managementsystem 608. The power management system 608 may be operatively connectedto a power distribution system 612 that distributes the electrical powerto electrical systems and components 614 of the spacecraft 600. Thepower management system 608 may regulate and/or covert the electricalpower for use by the electrical systems and components 614 of thespacecraft 600. The power management system 608 may include batteries616 for powering the electrical systems or components 614 or thebatteries may be a separate component. The power management system 608may recharge the batteries.

FIG. 7 is a flow chart of an example of a method 700 for recapturingenergy in accordance with an embodiment of the present disclosure. Inblock 702, a plurality of thermoelectric generator assemblies may bedistributed along an exterior surface of a thruster nozzle. Thethermoelectric generator assemblies may be similar to thermoelectricgenerator assemblies 116. The thermoelectric generator assemblies mayeach include multi-level TEG modules (TEMs). The TEMs may be similar toTEMs 118, 128 and 138 described herein. Each level of the TEMs mayinclude a plurality of TEG devices. A hot side of a first level orlowest level TEM of each thermoelectric generator assembly may bethermally coupled to an exterior surface of the nozzle using a thermallyconductive bonding agent, adhesive or similar material for thermallyattaching the thermoelectric generator assemblies to the nozzle tocapture waste heat from the nozzle. A cold side of a third level or toplevel TEM of each thermoelectric generator assembly may be exposed toambient air or, in another embodiment, the cold side of the top levelTEG module may be thermally coupled to a thermally conductive device.The thermally conductive device may be operatively connected to athermal management system similar to thermal management system 148described with reference to FIG. 2. Different types of TEG assembliesthat include different types of TEG devices may be used at differentlocations or distributed among different heat zones along the nozzlebased on a surface temperature along the nozzle to provide a highestefficiency of conversion of thermal energy to electrical energy duringoperation of the thruster. The different types of TEG assemblies mayalso each include different types of TEG devices in different levels orlayers of TEG modules to provide a highest efficiency of conversion ofthermal energy to electric energy in each level of TEG modules similarto that previously described.

In block 704, each of the TEG assemblies may be electrically connectedby an electrical wiring system. The electrical wiring system may includea power bus for electrically connecting the TEG assemblies to a powermanagement system and/or to a power distribution system. A powermanagement system may be provided to convert and regulate electricalpower generated by the TEG assemblies that is usable by systems andcomponents of a vehicle or spacecraft associated with the thruster. Theelectrical power may be distributed to the systems and components of thevehicle by the power distribution system. TEG assemblies may beelectrically connected in series with one another. The TEG moduleswithin each TEG assembly may also be electrically connected in series.

In block 706, a layer of material may be applied covering the TEGassemblies and at least a portion of the electrical wiring system toprotect the system from radiation and moisture. The layer of materialmay also include properties that prevent electrostatic discharge.

In block 708, waste heat may be captured from the nozzle by the TEGassemblies by transferring the waste heat from the exterior surface ofthe nozzle to a hot side of a first level or lowest level TEG module andthen transferring heat through each level TEG module to a cold side ofthe highest level TEG module of each of the TEG assemblies duringoperation of the thruster to convert the waste heat to electrical power.

In block 710, waste heat captured from the nozzle by the TEG assembliesmay be converted to electrical power by the TEG assemblies. Electricalpower may be generated by a temperature differential between the hotside and a cold side of the TEG devices of each of the TEG assemblies asdescribed herein.

In block 712, electrical power generated by the TEG assemblies may betransmitted to a power management system and/or power distributionsystem by a power bus. In block 714, electrical power may be distributedto the components and systems of a vehicle by the power distributionsystem.

The flowchart and block diagrams in the Figures illustrate thearchitecture, functionality, and operation of possible implementationsof systems, methods, and computer program products according to variousembodiments of the present invention. In this regard, each block in theflowchart or block diagrams may represent a module, segment, or portionof instructions, which comprises one or more executable instructions forimplementing the specified logical function(s). In some alternativeimplementations, the functions noted in the block may occur out of theorder noted in the figures. For example, two blocks shown in successionmay, in fact, be executed substantially concurrently, or the blocks maysometimes be executed in the reverse order, depending upon thefunctionality involved. It will also be noted that each block of theblock diagrams and/or flowchart illustration, and combinations of blocksin the block diagrams and/or flowchart illustration, can be implementedby special purpose hardware-based systems that perform the specifiedfunctions or acts or carry out combinations of special purpose hardwareand computer instructions.

The terminology used herein is for the purpose of describing particularembodiments only and is not intended to be limiting of embodiments ofthe invention. As used herein, the singular forms “a”, “an” and “the”are intended to include the plural forms as well, unless the contextclearly indicates otherwise. It will be further understood that theterms “comprises” and/or “comprising,” when used in this specification,specify the presence of stated features, integers, steps, operations,elements, and/or components, but do not preclude the presence oraddition of one or more other features, integers, steps, operations,elements, components, and/or groups thereof.

The corresponding structures, materials, acts, and equivalents of allmeans or step plus function elements in the claims below are intended toinclude any structure, material, or act for performing the function incombination with other claimed elements as specifically claimed. Thedescription of the present invention has been presented for purposes ofillustration and description, but is not intended to be exhaustive orlimited to embodiments of the invention in the form disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of embodiments ofthe invention. The embodiment was chosen and described in order to bestexplain the principles of embodiments of the invention and the practicalapplication, and to enable others of ordinary skill in the art tounderstand embodiments of the invention for various embodiments withvarious modifications as are suited to the particular use contemplated.

Although specific embodiments have been illustrated and describedherein, those of ordinary skill in the art appreciate that anyarrangement which is calculated to achieve the same purpose may besubstituted for the specific embodiments shown and that embodiments ofthe invention have other applications in other environments. Thisapplication is intended to cover any adaptations or variations of thepresent invention. The following claims are in no way intended to limitthe scope of embodiments of the invention to the specific embodimentsdescribed herein.

What is claimed is:
 1. A system for recapturing energy, comprising: athermoelectric generator assembly configured for thermally attaching toa surface heated by one of plasma heating and ionization heating, thethermoelectric generator assembly comprising: a first levelthermoelectric generator module, the first level thermoelectricgenerator module comprising a hot side that is thermally attached to thesurface, a cold side opposite to the hot side and a plurality ofthermoelectric generator devices disposed between the hot side and thecold side, the plurality of thermoelectric generator devices generatesan electric current based on a temperature differential across each ofthe plurality of thermoelectric generator devices; a second levelthermoelectric generator module stacked on the first levelthermoelectric generator module, the second level thermoelectricgenerator module comprising a hot side thermally attached to the coldside of the first level thermoelectric generator module, a cold sideopposite to the hot side and a plurality of thermoelectric generatordevices disposed between the hot side and the cold side, the pluralityof thermoelectric generator devices generates an electric current basedon a temperature differential across each of the plurality ofthermoelectric generator devices; and an electrical wiring system thatelectrically connects the second level thermoelectric generator moduleto the first level thermoelectric generator module and supplies theelectric current generated by the first level thermoelectric generatormodule and the second level thermoelectric generator module to anelectrical power apparatus.
 2. The system of claim 1, comprising a thirdlevel thermoelectric generator module stacked on the second levelthermoelectric generator module, the third level thermoelectricgenerator module comprising a hot side thermally attached to the coldside of the second level thermoelectric generator module, a cold sideopposite the hot side and a plurality of thermoelectric generatordevices disposed between the hot side and the cold side, the pluralityof thermoelectric generator devices generates an electric current basedon a temperature differential across the plurality of thermoelectricgenerator devices, the third level thermoelectric generator module beingelectrically connected to the second level thermoelectric generatormodule by the electrical wiring system and the first levelthermoelectric generator module, the second level thermoelectricgenerator module and the third level thermoelectric generator module arearranged in a triple stack configuration using a pyramid geometry forincreased temperature differential across each of the thermoelectricgenerator modules, wherein an area of the hot side and the cold side ofeach of the thermoelectric generator modules decreases from the firstlevel thermoelectric generator module to the third level thermoelectricgenerator module.
 3. The system of claim 2, wherein the first levelthermoelectric generator module, the second level thermoelectricgenerator module and the third level thermoelectric generator module areelectrically connected in series.
 4. The system of claim 2, wherein eachof the first level, second level and third level thermoelectricgenerator modules comprise a different type of thermoelectric generatordevice, the different type of thermoelectric generator device of each ofthe first level, second level and third level thermoelectric generatormodules is configured to generate a predetermined level of electricalpower based on a temperature on the hot side of each respectivethermoelectric generator module and a temperature differential betweenthe hot side and the cold side of each respective thermoelectricgenerator module.
 5. The system of claim 2, wherein each of the firstlevel, second level and third level thermoelectric generator modulescomprise a different type of thermoelectric generator device based on anefficiency in converting thermal energy to electrical energy accordinglyto a temperature on the hot side of each respective thermoelectricgenerator module and a temperature differential between the hot side andthe cold side of each respective thermoelectric generator module.
 6. Thesystem of claim 2, further comprising a thermally conductive devicethermally attached to the cold side of the third level thermoelectricgenerator module, the thermally conductive device being configured forconnecting to a thermal management system.
 7. The system of claim 2,further comprising a layer of material covering the thermoelectricgenerator modules and at least a portion of the electrical wiringsystem, the layer of material being configured to protect the systemfrom radiation and moisture and to prevent electrostatic discharge fromthe system.
 8. The system of claim 1, wherein the first levelthermoelectric generator module and the second level thermoelectricgenerator module comprise a curved configuration that corresponds to acontour of the surface.
 9. The system of claim 8, wherein the firstlevel thermoelectric generator module and the second levelthermoelectric generator module comprise flexible materials that allowthe first level and second level thermoelectric generator modules toflex with any movement of the surface.
 10. The system of claim 1,wherein the second level thermoelectric module is thermally attached tothe first level thermoelectric module and the first level thermoelectricgenerator module is thermally attached to the surface by a thermallyconductive bonding agent that comprises properties to preventelectrostatic discharge.
 11. The system of claim 1, wherein the surfaceis an exterior surface a nozzle of a thruster, wherein the thrustercomprises one of an electromagnetic thruster, an electrostatic thruster,an electrothermal thruster and the nozzle comprises an intake and anexhaust.
 12. The system of claim 11, further comprising a plurality ofthermoelectric generator assemblies distributed about the exteriorsurface of the nozzle, wherein the thermoelectric generator assembliescomprise different types of thermoelectric generator devices used indifferent heat zones along an axis of the nozzle to provide efficientconversion of thermal energy to electrical energy.
 13. A system forrecapturing energy, comprising: a thruster comprising a nozzle, whereinthe nozzle is heated by plasma heating or ionization heating ofpropellant gases being discharged through the nozzle; a plurality ofthermoelectric generator assemblies, each thermoelectric generatorassembly comprising: a first level thermoelectric generator module, thefirst level thermoelectric generator module comprising a hot sidethermally attached to an exterior surface of the nozzle, a cold sideopposite to the hot side and a plurality of thermoelectric generatordevices disposed between the hot side and the cold side, the pluralityof thermoelectric generator devices generates an electric current basedon a temperature differential across each of the plurality ofthermoelectric generator devices; a second level thermoelectricgenerator module stacked on the first level thermoelectric generatormodule, the second level thermoelectric generator module comprising ahot side thermally attached to the cold side of the first levelthermoelectric generator module, a cold side opposite to the hot sideand a plurality of thermoelectric generator devices disposed between thehot side and the cold side, the plurality of thermoelectric generatordevices generates an electric current based on a temperaturedifferential across each of the plurality of thermoelectric generatordevices; and an electrical wiring system that electrically connects theplurality of thermoelectric generator assemblies to a power managementsystem.
 14. The system of claim 13, comprising a third levelthermoelectric generator module stacked on the second levelthermoelectric generator module, the third level thermoelectricgenerator module comprising a hot side thermally attached to the coldside of the second level thermoelectric generator module, a cold sideopposite the hot side and a plurality of thermoelectric generatordevices disposed between the hot side and the cold side, the pluralityof thermoelectric generator devices generates an electric current basedon a temperature differential across the plurality of thermoelectricgenerator devices, the third level thermoelectric generator module beingelectrically connected to the second level thermoelectric generatormodule by the electrical wiring system and the first levelthermoelectric generator module, the second level thermoelectricgenerator module and the third level thermoelectric generator module arearranged in a triple stack configuration using a pyramid geometry forincreased temperature differential across each of the thermoelectricgenerator modules, wherein an area of the hot side and the cold side ofeach of the thermoelectric generator modules decreases from the firstlevel thermoelectric generator module to the third level thermoelectricgenerator module.
 15. The system of claim 14, wherein each of the firstlevel, second level and third level thermoelectric generator modulescomprise a different type of thermoelectric generator device based on aefficiency in converting thermal energy to electrical energy accordinglyto a temperature on the hot side of each respective thermoelectricmodule and a temperature differential between the hot side and the coldside of each respective thermoelectric generator module.
 16. The systemof claim 14, wherein the first level thermoelectric generator module,the second level thermoelectric generator module and the third levelthermoelectric generator module comprise a curved configuration thatcorresponds to a contour of the exterior surface of the nozzle.
 17. Amethod for recapturing energy, comprising: thermally attaching aplurality of thermoelectric generator modules to an exterior surface anozzle of a thruster, wherein the nozzle is heated by plasma heating orionization heating of propellant gases being discharged through thenozzle, each thermoelectric generator module comprising: a first levelthermoelectric generator module, the first level thermoelectricgenerator module comprising a hot side thermally attached to an exteriorsurface of the nozzle, a cold side opposite to the hot side and aplurality of thermoelectric generator devices disposed between the hotside and the cold side, the plurality of thermoelectric generatordevices generates an electric current based on a temperaturedifferential across each of the plurality of thermoelectric generatordevices; a second level thermoelectric generator module stacked on thefirst level thermoelectric generator module, the second levelthermoelectric generator module comprising a hot side thermally attachedto the cold side of the first level thermoelectric generator module, acold side opposite to the hot side and a plurality of thermoelectricgenerator devices disposed between the hot side and the cold side, theplurality of thermoelectric generator devices generates an electriccurrent based on a temperature differential across each of the pluralityof thermoelectric generator devices; and an electrical wiring systemthat electrically connects the plurality of thermoelectric generatorassemblies to a power management system; capturing waste heat from thenozzle by the plurality of thermoelectric generator assemblies; andconverting the captured waste heat by the plurality of thermoelectricgenerator assemblies into electrical power.
 18. The method of claim 17,further comprising providing a third level thermoelectric generatormodule stacked on the second level thermoelectric generator module, thethird level thermoelectric generator module comprising a hot sidethermally attached to the cold side of the second level thermoelectricgenerator module, a cold side opposite the hot side and a plurality ofthermoelectric generator devices disposed between the hot side and thecold side, the plurality of thermoelectric generator devices generatesan electric current based on the temperature differential across theplurality of thermoelectric generator devices, the third levelthermoelectric generator module being electrically connected to thesecond level thermoelectric generator module by the electrical wiringsystem and the first level thermoelectric generator module, the secondlevel thermoelectric generator module and the third level thermoelectricgenerator module are arranged in a triple stack configuration using apyramid geometry for increased temperature differential across each ofthe thermoelectric generator modules, wherein an area of the hot sideand the cold side of each of the thermoelectric generator modulesdecreases from the first level thermoelectric generator module to thethird level thermoelectric generator module.
 19. The method of claim 17,further comprising: thermally attaching a thermally conductive device tothe cold side of the third level thermoelectric generator module;thermally connecting the thermally conductive device to a thermalmanagement system; and applying a layer of material covering thethermoelectric generator modules and at least a portion of theelectrical wiring system, the layer of material comprising properties toprotect the system from radiation and moisture and to preventelectrostatic discharge.
 20. The method of claim 18, further comprising:transmitting the electrical power to a power distribution system; anddistributing the electrical power to components and systems of a vehicleby the power distribution system.